She decided to kill the 14-month-old dog she was training to hunt birds when it attacked chickens, an understandable mistake for a young dog IMO, and bit her once when she grabbed it's collar (no word on how seriously). She killed a goat by shooting it twice because she didn't like it, calling it mean and smelly. Apparently she's also recently put down 3 horses for unspecified reasons.
She deliberately included it in her new book "to illustrate her willingness, in politics as well as in South Dakota life, to do anything 'difficult, messy and ugly' if it simply needs to be done." When criticized she said, "I guess if I were a better politician I wouldn’t tell the story here.”
Sometimes animals do need to be euthanized, but it's rarely a first choice. Animal lovers and those who hunt with dogs have not been kind in their appraisals of the decisions. It's just a meme and maybe I don't need to worry, but her talk about carrying that attitude into politics puts me off.
Finally, Trump is old, unhealthy and there's fears he's showing signs of dementia. So this time VP choice might really matter a few years down the road.
They are much younger, meaning more malleable, and are also exhibiting different behavioural patterns.
This is a good point, but unfortunately it is the case that pets often have to suffer the consequences of their owner's insufficient knowledge and experience. She trained a dog for a purpose that requires her to be able to control it, without actually building the relation with the animal to attain this.
The owner has a responsibility to prevent this before it happens. If there are early signs and the owner cannot control the dog, they have to find another solution rather than hope for the best on the expense of a child who may be mildly to seriously hurt and develop a lifelong traumatic fear of dogs.
She had it for 1.4 years, of course she has attempted (unsuccessfully and probably not extinguishing all options) to rectify its behaviour. The owner's limitations will hurt the dog, but it is right to recognize that their relation should stop. There could potentially be a third solution that included placing it for adoption, but the majority of animal lovers that you mention in the sentence
do not really want to adopt a dog that is not still a puppy because it is not "cute enough" and not malleable enough, precisely one of the issues that distinguishes this situation (to my knowledge) from your anecdotal story.
I get that she is probably a shitty person who wants to do wrong things without further justification other than "somebody had to do it and I am such a person". However, I detest anything resembling the infantile moral judgement in the style of Hollywood, where the definite evaluation of good and bad characters are by how they treat a dog. Dogs are not that special.